Treatment of clay



Patented June 15, 1926.

UNITED STATES WILLIAM FELDENHEIMER, OF LONDON. ENGLAND.

TREATMENT OF CLAY.

No Drawing. Application filed June 16, 1925, Serial No. 37,467, and inGreat Britain August 7, 1824.

The present invention relates to the treatment of clays for theirpurification and the improvement of their colour, the presentapplication being a continuation in part of my copending application,Serial No. 681,820,

filed December th. 1923.

For a number of applications. for example. for papcrmanufacture. thevalue of clays depends upon their colour. and certain clays, 19 of whichsome of the Georgia clays constitute examples. have been unutilizable onaccount of their natural colour. The modes of treatment hithertosuggested for improving the colour of such clays have not been entirelysuccessful; and many substances which have been proposed as bleachingagents or colour improvers for clays, oxalic acid for instance-have beenfound impracticable for commercial working by 20 reason of cost. As aresult. most of the clays for uses in which good colour is a desideratumhave been imported. The present invention has been developed withGeorgia clays of the type aforesaid, and has for a 2 primary object toprovide an economical means for improving-the colour of these and likeclays.

According to this invention. a process for the treatment of clay ischaracterized by subjectin'g the clay in aqueous suspension to theaction of a plurality of bleaching agents.

The clay may be treated with two or more of such agents eithersimultaneously or successively, as may prove convenient in any givencase.

I have found that a bleaching agent for clay, such as oxalic acid, whenused in con junction with a co-operative bleaching agent provides ableaching process of improved economy and efliciency. For instance, toobtain substantially the same bleaching efiect as that produced by acomparatively expensive reagent as oxalic acid, less of such reagent isnecessary when using another suitable bleaching agent in conjunctionwith the acid. Moreover, by the use according to this invention of adual bleaching agent, the total quantity of reagent required to effect agiven result may be less than the quantity requisite when one of thecooperative reagents alone is employed even when used more than once.

There are also certain clays upon which individual reagents have noappreciable action.

For example, on some clays oxalic acid by itself will not efiect anymaterial improvement in colour, nor will sodium sulphide when employedalone. When. however, these two reagents are employed in conjunction, animmediate improvement in colour is attained.

If a clay be treated with an aqueous solution of sodium sulphide, or ofcalcium sulphide in caustic soda, the colour of the clay becomes greenor black on standing. This colour is at once discharged by the strongaclds, sulphuric, nitric, or hydrochloric acid, pr by per-salts orhydrogen peroxide; but marearly every case the clay returns to itsoriginal colour, and hence is still unbleached. On the other hand, ifthe sulphided clay be treated with a reducing acid, such as oxalic acid,the green or black colouration is destroyed, the clay is bleached at thesame time, and retains its improved colour after drying.

The aforesaid effects are, of course, influenced by the peculiarities ofdifierent clays; for a given reagent will not necessarily act in thesame way or to the same degree on different clays; but with due re gardto this fact the dual reaction may be said to besomething more thanmerely additive, and a feature of the invention to reside in thetreatment of clay with a plurality of bleaching agents the co-operativeeffect of which is greater than their individual effects.

One class of co-operative reducing agents according to this inventionare represented by soluble salts of reducing acids, examples being saltsof reducing sulphur-acids, such as, sodium sulphide, sodium sulphite,calcium sulphide in alkaline solution, sodium bisulphite, sodiumoxalate, sodium metabisulphite, sodium thiosulphate, sodiumhyposulphite.

The sodium'salts are preferred, as, apart from cost, I have found themto be more generally applicable and effective; potassium sulphide, forexample, being apparently of very much more limited a plication thansulphide of sodium, and faillng with a number of clays readily amenableto successful treatment with the latter reagent.

The other co-operative class of bleaching reagents consists of acids ofa reducing nature, and is exemplified by sulphurous acid and oxalicacid. Upon a number of clays tried, formic acid was without positiveresult. The preferred reagent of this class is oxalic acid, by reason ofits generally wide field of use and ease of application with goodresults.

The clay may be treated in aqueous sus pension with the reducing acid,such as oxalic acid, in the presence of, or after treatment with, theco-operative reagent, the fol lowing being examples of the manner inwhich the invention may be carried into effect:--

* *"EmampleI.

A Georgia clay from the Dry Branch District in suspension in water (20per cent clay, 80 per cent water) was run into settling tanks prior tofilter pressing in known manner. A solution in water of oxalic acid andsodium thiosulphate was prepared, the proand fifteen pounds sodiumthiosulphate per ton of clay. This solution was run in with the clayslip as the latter passed into the tanks. The clay was then allowed tosettle until the bleaching was effected, which in this case requiredsomewhat over forty-eight hours. The supernatant liquor was run off andthe clay dried as usual by filter-pressing. If desired the supernatantliquor after removal may be used again for the treatment of a freshbatch of clay, after suitable reinforcement with one or both of thereagents as required.

Example II.

A clay from the McIntyre District, Georgia, U. S. A., was treated,in'thesame way as in the preceding example, with a solution containing16 lbs. of oxalic acid and 16 lbs. of 30 per cent sodium sulphide perton of clay. After removal of the supernatant liquor the latter wasre-used several times before being discarded, on adding suflicient ofthe cheaper ordinary sodium sulphide'and hydrochloric acid to make theoxalic acid available for use again. The clay remained unbleached afterstanding more than 24 hours on addition of 24 pounds of oxalic acid perton of clay treated. It also remained unbleached after adding 24 poundsof sodium sulphide (60%) per ton of clay treated. 15 pounds of oxalic ac1d per ton of clay and 30 pounds in bisulphlte of soda per ton of claywi'll bleach this clay in about 36 hours: whereas neither of thesereagent-s alone will bleach the clay at the above mentionedconcentrations.

Emample II I In like manner, a Dry Branch clay from Georgia wassuccessfully bleached in a few days by treatment with sulphurous acidsimultaneously with sulphide of sodium and sodium thiosulphate, theproportions being 2 lbs. of 30 per cent sodium sulphide, 2 A),

Example IV.

The same day as in Example III was treated in aqueous suspension with asolution of calcium sulphide in sodium carbonate solution, andthereafter with sulphurous acid, in the proportions of 1 lb. of calciumsulphide, 8 lbs. of sodium carbonate V and 12.. lbs. of acommereialsolution of sulphurous acid per ton of the clay in a 20% suspension ofclay in water.

It may be" saidthat the results obtained by the use of sulphurous acidare not generally'so good or so readily obtainable as when oxalic acidis employed.

In order to purify the clay and at the same time to improve its colour,the second example just described may be carried out in a different way.The sodium sulphide may be introduced alone into the clay slip, wherebythe clay is deflocculated. The impurities can then be removed in knownmanner, and the oxalic acid solution subsequently added with a resultantimprovement of colour in the course of settling. Sodium oxalate is anexample of another reagent which may be employed with certain clays inorder to effect purification by defiocculation as a step in the processof decolorizing.

Where the co-operative reagent used for efiecting the deflocculation isone which with 1 a particular clay displays narrow working limits ofconcentration, a compatible defiocculating agent may be added or used byitself alone. For instance, sodium sulphide sodium 10 One tone of aGeorgia clay was mixed with four tons of water, and there were thenincorporated with the mixture 2 lbs. of 60 per cent sodium sulphide and2% lbs. of oxalic acid, whereby the clay was deflocculated. Afterseparation of the undeflocculated impurities, the remainder of theoxalic acid and sodium sulphide is added to complete the bleaching,making a total of six pounds of sodium sulphide (60%), and ten pounds ofoxalic acid per ton of clay. Using 30 pounds of oxalic acid it was foundthat over thirty pounds of oxalic acid per ton of clay treated did notbleach the clay to any material extent after standing over thirty-sixhours. Neither did 30 pounds of sodium sulphide (60%) per ton III ofclay treated required to complete the bleaching process was added.

I claim 1. The process for the treatment of clay which comprisessubjecting the clay in aqueous suspension to the action of a pluralityof bleaching agents the cooperative effect of which is greater than thesum of their individual effects.

2. The process for the treatment of clay which comprises subjecting theclay in aqueous suspension to the action of a plurality of reducingagents.

3. The process for the treatment of clay which comprises subjecting theclay in aqueous suspension to the action of a plurality of reducingagents, the cooperative effect of which is greater than the sum of theirindividual eflects.

4.. The process for the treatment of clay which comprises subjecting theclay in aqueous suspension to the action of an acid of reducingproperties and the sodium salt of a reducing sulphur acid.

5. The process for the treatment of clay which comprises subjecting theclay in aqueous suspension to the action of oxalic acid in co-operationwith the sodium salt of a reducing acid.

6. The process for the treatment of clay which comprises subjecting theclay in aqueous suspension to the action of oxalic acid in co-operationwith sodium sulphide.

7. In the treatment of clay, the steps consisting of purifying the clayby deflocculation and bleaching it by a reducing agent.

8. In the treatment of clay, the steps consisting of purifying the clayin aqueous suspension by a deflocculator and bleaching it by a reducingagent.

9. In the treatment of clay, the steps consisting of deflocculating theclay inaqueous suspension by an alkali deflocculator and then bleachingit by a reducing agent.

10. The process for the treatment of clay which comprises subjecting theclay in aqueous suspension to the simultaneous action of oxalic acid andsodium sulphide.

11. The process for the treatment of clay which comprises defiocculatingthe clay as a step in the bleaching thereof by initiall treating theclay in aqueous suspension with a co-operative bleaching reagent ofdeflocculating propert and, after removal of an undeflocculateimpurities, treating the clay suspension with another cooperativebleaching reagent to complete the bleaching.

12. The process for the treatment of clay which comprises deflocculatingthe clay as a step in the bleaching thereof by initiall treating theclay in aqueous suspension with sodium sulphide and, after removal ofany undeflocculated impurities, treating the clay suspension with oxalicacid.

- In testimony whereof I ailix my signature.

WILLIAM FELDENHEIMER.

